System and method for enhanced watch dog in solar panel installations

ABSTRACT

A system and method for automated shutdown, disconnect, or power reduction of solar panels. A system of solar panels includes one or more master management units (MMUs) and one or more local management units (LMUs). The MMUs are in communication with the LMUs with the MMUs and LMUs “handshaking” when the system is in operation. The MMUs are connected to one or more controllers which in turn are connected to emergency detection sensors. Upon a sensor detection of an emergency, the associated MMU is notified which in turn instructs associated LMUs to take appropriate action. In the event that communication with the MMUs has been cut off, the LMUs take the initiative to shut down, disconnect, or reduce the output of associated string(s) of solar panels.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/899,351 filed Jun. 11, 2020 which is a continuation of U.S.patent application Ser. No. 16/293,514, filed Mar. 5, 2019, issued asU.S. Pat. No. 10,686,403 on Jun. 16, 2020, which is a continuationapplication of U.S. patent application Ser. No. 15/717,244, filed Sep.27, 2017 and issued as U.S. Pat. No. 10,256,770 on Apr. 9, 2019, whichis a continuation application of U.S. patent application Ser. No.15/203,713, filed Jul. 6, 2016 and issued as U.S. Pat. No. 9,813,021 onNov. 7, 2017, which is a continuation application of U.S. patentapplication Ser. No. 14/473,659, filed Aug. 29, 2014 and issued as U.S.Pat. No. 9,397,612 on Jul. 19, 2016, which is a continuation applicationof U.S. patent application Ser. No. 13/092,783, filed Apr. 22, 2011 andissued as U.S. Pat. No. 8,823,218 on Sep. 2, 2014, which claims thebenefit of the filing date of Prov. U.S. Pat. App. Ser. No. 61/343,155,filed Apr. 22, 2010, entitled “System and Method for Enhanced Watch Dogin Solar Panel Installations,” where U.S. patent application Ser. No.13/092,783 is a continuation-in-part application of U.S. patentapplication Ser. No. 12/254,780, filed Oct. 20, 2008 and issued as U.S.Pat. No. 7,884,278 on Feb. 8, 2011, which claims the benefit of filingdate of Prov. U.S. Pat. App. Ser. No. 61/001,587, filed Nov. 2, 2007,where U.S. patent application Ser. No. 13/092,783 is also acontinuation-in-part application of U.S. patent application Ser. No.12/411,317, filed Mar. 25, 2009 and issued as U.S. Pat. No. 7,602,080 onOct. 13, 2009, which claims the benefit of filing date of Prov. U.S.Pat. App. Ser. No. 61/200,601, filed Dec. 2, 2008, where U.S. patentapplication Ser. No. 13/092,783 is also a continuation-in-partapplication of U.S. patent application Ser. No. 12/628,977, filed Dec.1, 2009 and issued as U.S. Pat. No. 8,933,321 on Jan. 13, 2015, whichclaims the benefit of filing dates of Prov. U.S. Pat. App. Ser. No.61/275,977, filed Sep. 3, 2009, and Prov. U.S. Pat. App. Ser. No.61/276,753, filed Sep. 16, 2009, the entire contents of whichapplications are hereby incorporated by reference as if fully set forthherein.

COPYRIGHT NOTICE AND PERMISSION

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the patent and trademarkoffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

FIELD OF INVENTION

The present invention relates to the field of electrical safeguards forphotovoltaic systems.

BACKGROUND

When a photovoltaic panel or laminate is exposed to direct or diffuselight, a lethal voltage potential may be present. In the United Statesthe possible voltage could be as high as 600 volts, while in Europe andthe rest of the world this voltage could approach a kilovolt.

Because of this potential danger from electrical shock, solar panelmanufacturers and code and standards development organizations have madesome recommendations to minimize or eliminate this danger.

One suggestion has been to cover the photovoltaic panel with an opaquematerial such as a tarpaulin. However, this approach proposes its ownsafety risk from having the wind catch the tarpaulin and pullinstallation personnel off the roof as they try to control the unstablesheet material against the wind.

Another recommendation is to install and/or service the photovoltaicpanels at night when there is minimal risk of the panels beingenergized. This approach presents the potential safety risks associatedfrom working in a poorly lighted environment.

In addition to the potential personnel safety issues there are alsosignificant risks to equipment and hardware. Connecting or disconnectingenergized plugs can cause arcing and damage to these connectors,junction boxes, and other electrical components.

Solar system installers take a large guard band (or safety margin) tomake sure the voltages don't cross the 600V or 1000V limits in theUnited States and the European Union, respectively. That limitationinhibits them from installing more solar panel modules, often referredto as “modules” or “panels,” in series to reduce the cost of combinerboxes or string inverters. When solar modules are connected in series orin mesh configurations, there can be a problem in which weaker modulesnot only produce less energy but also affect other modules' capabilitiesto deliver energy in the same string or wiring section.

In solar panel installations it is often desirable to have additionalsafety for the operating environment and for personnel involved withmaintenance, etc. Of particular concern are certain portions of thewiring. If certain wires are disconnected, through theft, vandalism,accident, natural forces, or any other cause, voltages may rise to anunacceptable, even dangerous, level.

In addition to locally generated problems that can affect the safety ofthe system and or people working at or near the system, other, moreregionally created problems may cause safety issues, including, forexample, floods, forest fires or neighborhood fires, earthquakes,landslides, etc.

BRIEF SUMMARY OF THE INVENTION

Disclosed herein are embodiments of a system and method to monitor oneor more sensors for anomalies in the operation of a photovoltaic system.In the event of an anomaly, the system may shut down or modify theoperation of all or part of the system.

Also disclosed herein are embodiments of a watchdog system to monitorcommunication signals between a central controller and a localcontroller. If one or more communication signals are not properlyreceived, the watchdog system polls the central controller to determineif the breakdown in communication is transient. In addition, thewatchdog circuit may monitor the electrical signals to determine ifthere is an irregularity. The watchdog system may notify the localcontroller to shut down or modify the operation of any or all solarmodules if it determines that the breakdown in communication is eithernot transient or if the irregularity in the electrical signals ispersistent.

These and other objects and advantages of the present invention willbecome clear to those skilled in the art in view of the description ofthe best presently known mode of carrying out the invention and theindustrial applicability of the preferred embodiment as describedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments are illustrated by way of example and not limitation inthe figures of the accompanying drawings in which like referencesindicate similar elements.

FIG. 1 illustrates a solar panel having a safety switch according to oneembodiment.

FIGS. 2-5 illustrate a spring loaded safety switch for a photovoltaicpanel according to one embodiment.

FIGS. 6-7 illustrate a junction box with a reed switch for aphotovoltaic panel according to one embodiment.

FIG. 8 illustrates an optical sensor to control a safety switch for aphotovoltaic panel according to one embodiment.

FIG. 9 illustrates a solar panel having a safety switch controlled viaauxiliary wiring according to one embodiment.

FIGS. 10-12 illustrate local management units according to someembodiments.

FIG. 13 illustrates a photovoltaic system according to one embodiment.

FIG. 14 illustrates a solar panel according to one embodiment.

FIGS. 15-17 show methods to improve performance of a photovoltaic systemaccording to some embodiments.

FIG. 18 illustrates an embodiment of an energy production systemincluding a plurality of junction boxes each coupled between a solarmodule and a power bus.

FIG. 19 illustrates a solar module and a detail view of an embodiment ofa junction box.

FIG. 20 illustrates an embodiment of a junction box.

FIG. 21 illustrates an embodiment of a method of controlling the outputof a solar module.

FIG. 22 illustrates an embodiment of an energy production systemincluding a master management unit.

FIG. 23 shows an embodiment of an exemplary process residing a mastermanagement unit controlling the output of a solar module.

DETAILED DESCRIPTION

The following description and drawings are illustrative and are not tobe construed as limiting. Numerous specific details are described toprovide a thorough understanding. However, in certain instances, wellknown or conventional details are not described in order to avoidobscuring the description. References to one or an embodiment in thepresent disclosure are not necessarily references to the sameembodiment; and, such references mean at least one.

The use of headings herein are merely provided for ease of reference,and shall not be interpreted in any way to limit this disclosure or thefollowing claims.

Reference in this specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the disclosure. The appearances of the phrase “in one embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment, nor are separate or alternative embodimentsmutually exclusive of other embodiments. Moreover, various features aredescribed which may be exhibited by some embodiments and not by others.Similarly, various requirements are described which may be requirementsfor some embodiments but not other embodiments.

Reducing Safety Risks

One embodiment of the disclosure provides a method and system to reducethe safety risks during the shipment, installation and/or maintenance ofphotovoltaic systems, without introducing the risks associated withother approaches, such as covering them with an opaque material orworking on them at night.

In one embodiment, safety protection is provided via the inclusion of anormally closed switch integral to the panel junction box or integral tothe panel module when alternating current (AC) or direct current (DC)modules are used.

FIG. 1 illustrates a solar panel having a safety switch according to oneembodiment. In FIG. 1, a solar panel 10 (e.g., a photovoltaic panel)includes at least one solar cell 12 (e.g., a photovoltaic cell) togenerate power when exposed to direct or diffuse light, in some cases avoltage module 14 to adjust or regulate the output voltage (or in someother cases a current module to regulate current), and a switch 16 toselectively isolate the solar cell 12 from the output connectors of thesolar panel. In yet other cases, the switch may be incorporated intoregulator modules, such as voltage module 14.

In one embodiment, the switch 16 is a normally closed switch. During theshipment, installation and/or maintenance, the switch 16 is placed in anopen state to isolate the solar cell 12 from the output. After theinstallation or maintenance, the switch 16 is placed into a closed stateto allow the solar cell 12 to energize the output connectors of thesolar panel and to supply power through the output connectors of thesolar panel.

The switch 16 and the voltage module can be integrated into the junctionbox of the solar panel. In some embodiment, the switch 16 is integratedwith the voltage module 14 as a panel module.

FIGS. 2 through 5 illustrate a spring loaded safety switch for aphotovoltaic panel according to one embodiment. In FIGS. 2 through 5,the switch includes two contactors 102 and 103 made of a conductivemetal or plated hybrid. The contactors 102 and 103 are normally made ofa spring alloy metal or have an integral spring plunger design (notshown). The contactors 102 and 103 are positioned or fixed in such a waythat the two contacts 102 and 103 are spring loaded toward each other tomaintain electrical continuity between the two contactors 102 and 103.Thus, the switch is normally closed (NC) and not in a safe mode forinstallation or maintenance.

In FIG. 2, a safe mode for installation or maintenance is achieved whenthe blade 104 is inserted between the two contactors 102 and 103. Theblade 104 is manufactured from a dielectric material and when insertedbetween the two contactors 102 and 103 there is no electrical continuitybetween the contactors 102 and 103.

As illustrated in FIG. 2, the blade 104 may also have a flag 105attached. The flag 105 could be red or some other highly visible color,to provide a visual indicator of the state of the panel.

In one embodiment, the panels and/or panel with integral modules wouldcome shipped from the factory with the blade 104 and the flag 105, wherethe blade 104 is inserted between the two contactors 102 and 103. Thepanels would be installed and integrated with the blade 104 present andflag 105 visible. The installer would mount, secure, and plug in all ofthe connections in the system, including the grounding.

As illustrated in FIG. 3, once the installation is completed theinstaller would remove the blades 104 at all those places indicated bythe flags 105. Once the blade 104 is removed, the spring loadedcontactors 102 and 103 contact each other to provide an electric pathfrom the photovoltaic cells to the output connectors of the photovoltaicpanel.

If additional work or troubleshooting were needed, the blade(s) 104 andflag(s) 105 could be reinserted, aided by the tapered section 207 of theblade 104, thereby breaking the electrical continuity between thecontactors 102 and 103 at point 206.

In some embodiments, there is symmetry in contactors 102 and 103. Inother embodiments, the contactors 102 and 103 are not identical or evensimilar. The contactors 102 and 103 are made of electrically conductivematerial and configured to be in physical contact with each so that anelectrically conductive path 206 is maintained, after the blade 104 isremoved. In at least some embodiments, the electrical conductive path206 is maintained without the blade 104 being inserted between thecontactors 102 and 103, then disrupted by the blade 104 inserted betweenthe contactors 102 and 103, and then reestablished by the reinsertionsof a dielectric device such as the blade 104.

In addition to the visual indication of the modes of the panels providedby the flag(s) 105, the flags could also provide information in the formof text, such as, for example, “Remove before operation” or a warning ofpotentially lethal voltage.

FIG. 4 illustrates a configuration of a spring loaded switch integratedwith a junction box 308 of a photovoltaic panel. The junction box 308includes a connector to connect the solar power generated by thephotovoltaic panel to a load (e.g., an inverter, a voltage bus, etc.)via a cable 307. Thus, when the blade 104 is inserted into the switch,with the flag 105 visible, the voltage generated by the solar cells isisolated from the connector for the cable 307; and thus it is safe toinstall the photovoltaic panel or to perform maintenance operations onthe photovoltaic panel.

FIG. 5 shows the components of the spring loaded switch and the junctionbox of a photovoltaic panel. As illustrated in FIG. 5, the junction box308 has an opening 409, which provides access to remove the blade 104and/or to re-insert the blade 104. The contactors 103 of the switch canbe attached to the junction box 308 via fastening the portion 401 to asupporting member of the junction box 308, such as a printed circuitboard (PCB).

FIGS. 6 through 7 illustrate a junction box with a reed switch for aphotovoltaic panel according to one embodiment. FIG. 6 shows an assemblyof a reed switch 510 and magnets for integrated into the photovoltaicjunction box 308. FIG. 7 shows a cut-away section illustrating the reedswitch 510 and the magnets 511 and 512 installed within the portion 509of the junction box 308.

In FIG. 7, a reed switch 510 is made normally closed by integrating astationary biasing magnet 511 into the junction box 308 in closeproximity to the normally open reed switch, so that the switch 510 isclosed in absence of the magnet 512.

In one embodiment, the magnet 512 is inserted into the junction box well509 so that the reversed polarity cancels the magnetic lines of forceand the reed switch 510 opens.

In one embodiment, the magnet 512 is installed in the junction box well509 at the factory; and a flag 105 (not shown in FIGS. 6 and 7) isattached to the magnet 512. The magnet 512 is removable and/orre-insertable via the junction box well 509.

In other embodiments, normally closed (NC) reed contacts can be used toreplace the normally open (NO) reed contacts 510 and the magnet 511,avoiding the need for the additional stationary magnet.

Once the installation and integrations are complete the magnet 512 isremoved and may be discarded. The power leads of the junction box 308can then be energized via the semiconductor switch or relay (not shown),when the reed switch 512 is in the closed state.

In some cases, a semiconductor switch (not shown in FIG. 7) can be usedto energize the power leads of the junction box 308. The panel junctionbox 308 or inverter (not shown in FIG. 7) may include a controller unitwith a watch dog circuit configured to send a signal periodically (e.g.,every time interval t) to maintain the connection of the panel outputsto the string. When this signal is timed-out or is absent, the paneloutputs of the panel are disconnected via a semiconductor switch device(not shown).

FIG. 8 illustrates an optical sensor to control a safety switch for aphotovoltaic panel according to one embodiment. In FIG. 8, an opticalsensor unit 700 with an optical sensor 701 is mounted on a printedcircuit board (PCB) 711. Additionally, springs 702 and 712 hold aseparator 703 in place that can be removed in direction of arrow 704using a pull-tab similar to the flag 105 discussed earlier. Not shown inFIG. 8 is the exterior enclosure that would contain the mechanicalelements such as the cable connections and the guide elements forguiding separator 703 in and out of the unit.

In one embodiment, additional circuitry (not shown in FIG. 8) will be onthe side of the PCB 711, such as a control circuit to affect an on/offswitching either in some cases by FET (Field-Effect Transistor)transistors or using, in other cases, a relay, such as a bi-stable relayor another suitable circuit. The operational power may be drawn from thesolar system itself, or it may be brought up by auxiliary wiring.

In yet some other embodiments, a relay can be simply remote controlledby an auxiliary wire to close or open the circuit. The advantage of thisapproach is that no pull-tabs (flags or blades) can be forgotten on theroof.

In one embodiment, a mechanism and/or circuitry is integrated in thepanel to identify the load from the inverter and connect the panel tothe panel outputs when the load is detected. When no load is present thepanel outputs is disconnected. This functionality would also beimplemented using a semiconductor switch device or other suitable device(such as a relay), and some sensor circuitry, allowing an automaticreconnect when the loop appears to be closed and a load connected.

FIG. 9 illustrates a solar panel having a safety switch controlled viaauxiliary wiring according to one embodiment. In FIG. 9, a separate wireis connected to control the switch 16 from a remote location. Forexample, the switch may be controlled via a signal from a watch dogcircuit, from a remote switch or controller, etc.

Balancing Solar Panels

When solar modules are connected in series or mesh configuration, therecan be a problem in which weaker modules not only produce less energybut also affect other modules in the same string or wiring section. Bymeasuring one can determine that a few modules are weaker than theothers in most commercially installed strings. Thus, the string isgenerating less power than the sum available at each module if moduleswere operated separately.

At least one embodiment of the present disclosure provides methods andsystems to switch on and off weak modules in the string in a way thatthe current on the string bus from the good modules won't be affected bythe weak modules.

FIGS. 10 through 12 illustrate local management units according to someembodiments. In FIGS. 10 through 12, local management units (1101) areused to switch on and off the solar module (1102) periodically toimprove the energy production performance of the photovoltaic systemsconnected, at least in part, in series.

In FIG. 10, a management unit (101) is local to the solar module (102)and can be used to periodically couple the solar module (102) to theserial power bus (103) via the switch Q1 (106), to improve the totalpower output for the string of solar modules connected to the serialpower bus in series.

The local management unit (LMU) (1101) may include a solar modulecontroller to control the operation of the solar module (1102) and/or alink module unit to provide connectivity to the serial power bus (1103)for energy delivery and/or for data communications.

In one embodiment, the command to control the operation of the switch Q1(1106) is sent to the local management unit (1101) over the photovoltaic(PV) string bus (power line) (1103). Alternatively, separate networkconnections can be used to transmit the data and/or commands to/from thelocal management unit (1101).

In FIGS. 10 and 11, the inputs (1104 a, 1104 b, 1104 c) to the localmanagement unit (1101) are illustrated separately. However, the inputs(1104 a, 1104 b, 1104 c) are not necessarily communicated to localmanagement unit (1101) via separate connections. In one embodiment, theinputs are received in the local management unit via the serial powerbus (1103).

In FIG. 10, the solar module (1102) is connected in parallel to thecapacitor C1 (1105) of the local management unit (1101). The diode D1(1107) of the local management unit (1101) is connected in series in theserial power bus (1103) which may or may not be part of an overall meshconfiguration of solar modules. The switch Q1 (1106) of the localmanagement unit can selectively connect or disconnect the solar module(102) and the capacitor C1 (1105) from a parallel connection with thediode D1 (1107) and thus connect or disconnect the solar module (1102)from the serial power bus (1103).

In FIG. 10, a controller (1109) of the local management unit (1101)controls the operation of the switch (1106) according to the parameters,such as duty cycle (1104 a), phase (1104 b) and synchronization pulse(1104 c).

In one embodiment, the controller (1109) receives the parameters (1104a, 1104 b, 1104 c) from a remote management unit via the serial powerbus (1103) or a separate data communication connection (e.g., a separatedata bus or a wireless connection). In some embodiment, the controller(1109) may communicate with other local management units connected onthe serial power bus (1103) to obtain operating parameters of the solarmodules attached to the serial power bus (1103) and thus compute theparameters (e.g., 1104 a and 1104 b) based on the received operatingparameters. In some embodiments, the controller (1109) may determine theparameter (e.g., 104 a and 104 b) based on the operating parameters ofthe solar module (1102) and/or measurements obtained by the controller(1109), without communicating with other local management units of othersolar modules, or a remote system management unit.

In FIG. 11, a system (100) has a local management unit (1101) coupled tothe solar module (1102). The local management unit (1101) is connectedbetween the solar module (1102) and the string bus (1103) to improve thetotal power output for the whole string on the serial power bus (1103).Commands to the local management unit (1101) can be sent over thephotovoltaic (PV) string bus (power line) (1103). To make the figureclearer, the inputs (1104 a, 1104 b, 1104 c) to the controller (1109) ofthe local management unit (1101) are drawn separately, which does notnecessarily indicate that the inputs (1104 a, 1104 b, 1104 c) areprovided via separate connections and/or from outside the localmanagement unit (1101). For example, in some embodiments, the controller(1109) may compute the parameters (1104 a, 1104 b, 1104 c) based onmeasurements obtained at the local management unit (1101), with orwithout data communications over the serial power bus (1103) (or aseparate data communication connection with other management units).

In FIG. 11, the local management unit (1101) is connected in one side tothe solar module (1102) in parallel and on the other side in series to astring of other modules, which may or may not be part of an overall meshconfiguration. The local management unit (1101) may receive, amongothers, three inputs or types of input data, including a) requested dutycycle (1104 a), which can be expressed as a percentage (e.g., from 0 to100%) of time the solar module (1102) is to be connected to the serialpower bus (1103) via the switch Q1 (1106), b) a phase shift (1104 b) indegrees (e.g., from 0 degree to 180 degree) and c) a timing orsynchronization pulse (1104 c). These inputs (e.g., 1104 a, 1104 b and1104 c) can be supplied as discrete signals, or can be supplied as dataon a network, or composite signals sent through the power lines orwirelessly, and in yet other cases, as a combination of any of theseinput types.

In FIG. 11, the local management unit (1101) periodically connects anddisconnects the solar module (1102) to and from the string that formsthe serial power bus (1103). The duty cycle (1104 a) and the phase (1104b) of the operation of the switch Q1 (1106) can be computed in a numberof ways to improve the performance of the system, which will bediscussed further below.

In FIG. 11, the local management unit (1101) includes a capacitor C1(1105) and a switch Q1 (1106), as well as a diode D1 (1107). In FIG. 11,the diode D1 (1107) is supplemented with an additional switch Q2 (1108),which acts as a synchronous rectifier to increase efficiency. In oneembodiment, the additional switch Q2 (1108) is open (turned off) whenthe switch Q1 (1106) is closed (turned on) to attach the solar module(1102) (and the capacitor C1 (1105)) to the serial power bus (1103).

In some cases, a filter (not shown), including a serial coil and aparallel capacitor, is also used. The filter may be placed at the localmanagement unit or placed just before the fuse box or inverter, or bepart of either one of those.

In FIG. 11, the controller (1109) is used to process the input signals(e.g., 1104 a, 1104 b, 1104 c) and drive the switches Q1 (1106) and Q2(1108). In one embodiment, the controller (1109) is a small single chipmicro controller (SCMC). For example, the controller (1109) may beimplemented using Application-Specific Integrated Circuit (ASIC) orField-Programmable Gate Array (FPGA). The controller (1109) can even beimplemented in discrete, functionally equivalent circuitry, or in othercases a combination of SCMC and discrete circuitry.

In one embodiment, the controller (1109) is coupled to the solar module(1102) in parallel to obtain power for processing; and the controller(1109) is coupled to the serial power bus (1103) to obtain signalstransmitted from other management units coupled to the serial power bus(1103).

By switching the module (1102) (or groups of cells, or a cell) on andoff to the string periodically, the local management unit (1101) maylower the voltage reflected to the string bus (1103) (e.g., a loweraverage voltage contributed to the string bus) and can cause the currentreflected to the string bus (1103) to be higher, nearer the level itwould be if the module was not weak, generating a higher total poweroutput.

In one embodiment, it is preferable to use different phases to operatethe switches in different local management units on a string to minimizevoltage variance on the string.

In FIG. 12, the local management unit (1101) provides two connectors(1112 and 1114) for serial connections with other local management unit(1101) to form a serial power bus (1103) (FIG. 11). The controller(1109) controls the states of the switches Q1 (1106) and Q2 (1108).

In FIG. 12, when the controller (1109) turns on the switch (1106), thepanel voltage and the capacitor C1 (1105) are connected in parallel tothe connectors (1112 and 1114). The output voltage between theconnectors (1112 and 1114) is substantially the same as the output panelvoltage.

In FIG. 12, during the period the switch (1106) is turned off (open),the controller (1109) turns on (closes) the switch (1108) to provide apath around the diode D1 (1107) to improve efficiency.

In FIG. 12, when the switch (1106) is turned off (open), the panelvoltage charges the capacitor C1 (1105), such that when the switch(1106) is turned on, both the solar panel and the capacitor (1105)provides currents going through the connectors (1112 and 1114), allowinga current larger than the current of the solar panel to flow in thestring (the serial power bus (1103)). When the switch (1106) is turnedoff (open), the diode D1 (1107) also provides a path between theconnectors (1112 and 1114) to sustain the current in the string, even ifthe switch (1108) is off for some reasons.

In one embodiment, the controller (1109) is connected (not shown in FIG.12) to the panel voltage to obtain the power for controlling theswitches Q1 (1106) and Q2 (1108). In one embodiment, the controller(1109) is further connected (not shown in FIG. 12) to at least one ofthe connectors to transmit and/or receive information from the string.In one embodiment, the controller (1109) includes sensors (not shown inFIG. 12) to measure operating parameters of the solar panel, such aspanel voltage, panel current, temperature, light intensity, etc.

FIG. 13 illustrates a photovoltaic system (1200) according to oneembodiment. In FIG. 13, the photovoltaic system 1200 is built from a fewcomponents, including photovoltaic modules (1201 a, 1201 b, . . . , 1201n), local management unit units (1202 a, 1202 b, . . . , 1202 n), aninverter (1203), and a system management unit (1204).

In one embodiment, the system management unit (1204) is part of theinverter (1203), the combiner box (1206), a local management unit, or astand-alone unit. The solar modules (1201 a, 1201 b, . . . , 1201 n) areconnected in parallel to the local management unit units (1202 a, 1202b, . . . , 1202 n) respectively, which are connected in series to form astring bus (1205), which eventually is connected to an inverter (1203)and the system management unit (1204).

In FIG. 13, the string bus (1205) can be connected to the inverter(1203) directly or as part of a mesh network or combiner boxes or fuseboxes (not shown). An isolated local management unit can be used as acombiner box (1206) to adjust all voltages before connecting to theinverter (1206); or, a single or multi-string inverter can be used. Tolimit the changes in the voltage of the bus, the system management unit(1204) may assign a different phase for each of the local managementunits (1202 a, 1202 b, . . . , 1202 n). In one embodiment, at any giventime, a maximum of a predetermined number of solar modules (e.g., onesingle solar module) are disconnected from the string bus (1205).

In one embodiment, beyond the module connection the local managementunits can have the signal inputs, including but not limited to dutycycle (1104 a), phase (1104 b) and synchronization pulse (1104 c) (e.g.,to keep the local management units synchronized). In one embodiment, thephase (1104 b) and the synchronization pulse (1104 c) are used tofurther improve performance, but the local management unit (1101) canwork without them.

In one embodiment, the local management unit may provide output signals.For example, the local management unit (1101) may measure current andvoltage at the module side and optionally measure current and voltage inthe string side. The local management unit (1101) may provide othersuitable signals, including but not limited to measurements of light,temperature (both ambient and module), etc.

In one embodiment, the output signals from the local management unit(1101) are transmitted over the power line (e.g., via power linecommunication (PLC)), or transmitted wirelessly.

In one embodiment, the system management unit (1204) receives sensorinputs from light sensor(s), temperature sensor(s), one or more each forambient, solar module or both, to control the photovoltaic system(1200). In one embodiment, the signals may also include synchronizationsignals. For example, a using the described methods the local managementunit can be a very non-expensive and reliable device that can easilyincrease the throughput of a photovoltaic solar system by a few (e.g.,signal or low double digits) percentage points. These varied controlsalso allow installers using this kind of system to control the VOC (opencircuit voltage) by, for example by shutting off some or all modules.For example, by using the local management units of the system, a fewmodules can be disconnected from a string if a string is getting to theregulatory voltage limit, thus more modules can be installed in astring.

In some embodiments, local management units can also be used within thesolar panel to control the connection of solar cells attached to stringsof cells within the solar panel.

FIG. 14 illustrates a solar panel according to one embodiment. In oneembodiment, the solar panel (1300) has a few strings of solar cells(e.g., three solar cell strings per module). In FIG. 14, a localmanagement unit (1101) can be applied to a group of cells (1301) withina string of an individual solar panel (1300), or in some cases to eachcell (1301) in a solar panel (1300).

In FIG. 14, a group of solar cells (1301) that are attached to a localmanagement unit (1101) may be connected to each other in series, inparallel, or in a mesh configure. A number of local management units(1101) connect the groups of the solar cells (1301) in a string toprovide output for the solar panel (1300).

Some embodiments of the disclosure includes methods to determine theduty cycles and/or phases for local management units connected to astring or mesh of solar modules.

In some embodiments, the duty cycle of all local management units in astring or mesh can be changed, to increase or decrease the stringvoltage. The duty cycles may be adjusted to avoid exceeding the maximumvoltage allowed. For example, the maximum voltage may be limited by thecombiner box (1206), the inverter (1203), or any other load connected tothe string bus (1205), or limited by any regulations applicable to thatsystem. In some embodiments, the duty cycles are adjusted to align thevoltage of multiple strings.

In some embodiments, the duty cycle of one local management unit (1101)in a string can be changed to cause higher current in that localmanagement unit (1101) and overall higher power harvesting.

In one embodiment, the duty cycles are computed for the solar modulesthat are connected to a string via the corresponding local managementunits. The duty cycles can be calculated based on the measured currentand voltages of the solar modules and/or the temperatures.

After an initial set of duty cycles is applied to the solar modules, theduty cycles can be further fine-tuned and/or re-adjusted to changes,such as shifting shading etc., one step at a time, to improve powerperformance (e.g., to increase power output, to increase voltage, toincrease current, etc.). In one embodiment, target voltages are computedfor the solar modules, and the duty cycles are adjusted to drive themodule voltage towards the target voltages.

The methods to compute the duty cycles of the solar modules can also beused to compute the duty cycles of the groups of solar cells within asolar module.

FIGS. 15 through 17 show methods to improve performance of aphotovoltaic system according to some embodiments.

In FIG. 15, at least one operating parameter of a solar energyproduction unit coupled to a string via a management unit is received(1401) and used to identify (1403) a duty cycle for the management unitto connect the solar energy production unit to string. The solar energyproduction unit may be a solar module, a group of solar cells within asolar module, or a single solar cell in a string in a solar module. Theduty cycle is adjusted (1405) to optimize the performance of the solarenergy production unit and/or the string.

For example, the duty cycle can be adjusted to increase the current inthe string and/or the solar energy production unit, to increase theoutput power of the string and/or the solar energy production unit, toincrease the voltage of the solar energy production unit, etc.

In FIG. 16, the operating voltages of a plurality of solar panelsconnected in series are received (1421) and used to identify (1423) asecond solar panel having the highest operating voltage (highest outputpower) in the string.

In FIG. 16, a duty cycle of a first solar panel is computed (1425) basedon a ratio in operating voltage between the first and second solarpanels. Alternatively, the duty cycle can be computed based on a ratioin output power between the first and second solar panels.Alternatively, the duty cycle can be computed based on a ratio betweenthe first and second solar panels in estimated/computed maximum powerpoint voltage. Alternatively, the duty cycle can be computed based on aratio between the first and second solar panels in estimated/computedmaximum power point power.

The duty cycle of the first solar panel is adjusted (1427) to improvethe performance of the first solar energy production unit and/or thestring, until a decrease in the operating voltage of the second solarpanel is detected. For example, the duty cycle of the first solar panelcan be adjusted to increase the total output power of the string, toincrease the current of the string, to increase the current of the firstsolar panel, to drive the voltage of the first solar panel towards atarget voltage, such as its maximum power point voltage estimated basedon its current operating parameters, such as temperature or a voltagecalculated using its estimated maximum power point voltage.

In FIG. 16, in response to the detected decrease in the operatingvoltage of the second solar panel which had the highest operatingvoltage, the adjustment in the duty cycle of the first solar panel thatcauses the decrease is undone/reversed (1429).

In FIG. 16, the duty cycle of the second solar panel is optionallydecreased (1431) to increase the operating voltage of the second solarpanel. In some embodiments, the strongest solar panel (or strong panelswithin a threshold from the strongest panel) is not switched off line(e.g., to have a predetermined duty cycle of 100%).

In one embodiment, the duty cycle of the second solar panel isrepeatedly decreased (1429) until it is determined (1431) that thedecrease (1429) in the duty cycle of the second solar panel cannotincrease the voltage of the second solar panel.

In FIG. 17, operating parameters of a plurality of solar panelsconnected in a string are received (1441) and used to identify (1443) afirst maximum power point voltage of a first solar panel. A second solarpanel having the highest operating voltage (or output power) in thestring is identified. A second maximum power point voltage of the secondsolar panel is identified (1447) based on the received operatingparameters and used to compute (1449) a target voltage for the firstsolar energy production unit. In one embodiment, the target voltage is afunction of the first and second maximum power point voltages and thehighest operating voltage identified (1445) in the second solar panel inthe string. The duty cycle of the first solar energy production unit isadjusted to drive the operating voltage of the first solar panel towardsthe target voltage.

Alternatively, the target voltage may be the set as the first maximumpower point voltage of the first solar panel.

In one embodiment, to adjust voltage a same factor is applied to allmodules in that string. For example, in a case of a first module A1 thatis producing only 80%, and the voltage of the whole string needs to be5% lower, the duty cycle of A1 is 80% multiplied the duty cycle appliedto the whole string (which is Y in this example) so module A1 then hasY×0.8 as duty cycle.

In some embodiments, the system management unit (1204) and/or the localmanagement units (e.g., 1202 a, 1202 b, . . . , 1202 n) are used solelyor in combination to determine the parameters to control the operationsof the switches.

For example, in one embodiment, a system management unit (1204) is the“brain” of the system, which decides on the duty cycle and phaseparameters.

For example, in another embodiment, each local management unitbroadcasts information to the other local management units on the stringto allow the individual local management units to decide their own dutycycle and phase parameters.

In some embodiment, a local management unit may instruct one or moreother local management units to adjust duty cycle and phase parameters.For example, the local management units on a string bus (1205) may electone local management unit to compute the duty cycle and phase parametersfor other local management units on the string.

For example, in some embodiment, the system management unit (1204) maydetermine one or more global parameters (e.g., a global duty cycle, themaximum power on the string, the maximum voltage on the string, etc.),based on which individual local management units adjust their own dutycycles.

In some embodiments, a local management unit may determine its own dutycycles without relying upon communicating with other management units.For example, the local management unit may adjust its duty cycle forconnecting its solar module to the string to operate the solar module atthe maximum power point.

In one embodiment, module voltage are measured by the local managementunits in the same string at substantially/approximately the same timeand used to identify the strongest solar module. A strongest solarmodule provides the most power in the string. Since the modules areconnected in series, the solar module having the highest module voltagein the string can be identified as the strongest solar module. In someembodiment, the operating voltage and current of the solar module aremeasured to determine the power of the solar module.

In one embodiment, after the highest module voltage Vm in the string isidentified, the duty cycle for each module can be computed as a functionof a ratio between the module voltage V of the module and the highestmodule voltage Vm. For example, the duty cycle for a module can becomputed as 1−((Vm−V)/Vm)=V/Vm.

In one embodiment, the system management (1204) may identify the highestmodule voltage from the module voltages received from the localmanagement units (1202 a, 1202 b, . . . , 1202 n), and compute the dutycycles for the corresponding local management units (1202 a, 1202 b, . .. , 1202 n).

In one embodiment, the local management units (1202 a, 1202 b, . . . ,1202 n) may report their module voltages on the string bus (1205) toallow individual local management units (1202 a, 1202 b, . . . , 1202 n)to identify the highest module voltage and compute the duty cycles,without relying upon the system management unit (1204).

In one embodiment, one of the local management units (1202 a, 1202 b,1202 n) may identify the highest module voltage and/or compute the dutycycles for the other local management units (1202 a, 1202 b, . . . ,1202 n).

In one embodiment, the duty cycles are determined and/or adjustedperiodically.

In one embodiment, after the duty cycles for the solar modules on thestring are set based on the module voltage ratio relative to the highestmodule voltage in the string, the duty cycles can be fine tuned toincrease the power performance. The duty cycles can be fine tuned onestep at a time, until a decrease of voltage of the module with thehighest power is detected. In response to the detected decrease, thelast change that caused the decrease can be reversed (undone). The finetuning of the duty cycles can be used to reach the peak performancepoint (e.g., for maximum power point tracking).

In one embodiment, after the strongest module is identified, the dutycycles of the solar modules on the string are adjusted until the modulewith the highest power in the string decrease its voltage. Sincedecreasing the duty cycle of a solar module decreases the time periodthe module is connected to the string and thus increases its voltage,the duty cycle of the module with the highest power in the string can bedecreased to increase its voltage, in response to the decrease in itsvoltage caused by the adjustment to the duty cycles of other solarmodules on the string. For example, the duty cycle of the module withthe highest power in the string can be decreased until its voltage ismaximized.

In one embodiment, the local management unit measures module and ambienttemperatures for some methods to determine the duty cycles. For example,the operating parameters measured at the local management units (e.g.,1202 a, 1202 b, . . . , 1202 n), such as module temperature, can be usedcompute the estimated voltages of the solar modules at their maximumpower points. For example, a formula presented by Nalin K. Gautam and N.D. Kaushika in “An efficient algorithm to simulate the electricalperformance of solar photovoltaic arrays”, Energy, Volume 27, Issue 4,April 2002, pages 347-261, can be used to compute the voltage Vmp of asolar module at the maximum power point. Other formulae can also beused. Once the maximum power point voltage Vmp of a solar module iscomputed or estimated, the duty cycle of the solar module connected to astring can be adjusted to drive the module voltage to thecomputed/estimated maximum power point voltage Vmp, since decreasing theduty cycle of a solar module normally increases its voltage.

In one embodiment, a local management unit may adjust the duty cycle ofthe solar module connected to the local management unit to change themodule voltage to the computed/estimated maximum power point voltageVmp, without having to communicating with other management units.

In one embodiment, a local management unit (or a system management unit)may adjust the duty cycle of the solar module connected to the localmanagement unit to perform maximum power point tracking.

In one embodiment, after identifying the strongest module andcomputing/estimating the maximum power point voltage Vmpm of thestrongest module, the duty cycle for each module on a string can becomputed as a function of a ratio between the maximum power pointvoltage Vmp of the module and the maximum power point voltage Vmpm ofthe strongest module. For example, the duty cycle for a module can becomputed as 1−((Vmpm−Vmp)/Vmpm)=Vmp/Vmpm. The duty cycle can beperiodically updated, based on the current operating parametersmeasured, and/or fine tuned until a decrease in the voltage of thestrongest module is detected.

Alternatively, a target voltage for each module on the string can becomputed as a function of a ratio between the maximum power pointvoltage Vmp of the module and the maximum power point voltage Vmpm ofthe strongest module. For example, the target voltage for a module canbe computed as Vm×Vmp/Vmpm, where Vm is the measured voltage of thestrongest module. The duty cycle of the module can be changed to drivethe module voltage of the module towards the target voltage.

In one embodiment, after identifying the strongest module andcomputing/estimating the maximum power point power Pmpm of the strongestmodule, the duty cycle for each module on a string can be computed as afunction of a ratio between the maximum power point power Pmp of themodule and the maximum power point power Pmpm of the strongest module.For example, the duty cycle for a module can be computed as1−((Pmpm−Pmp)/Pmpm)=Pmp/Pmpm. The duty cycle can be periodicallyupdated, based on the current operating parameters measured, and/or finetuned until a decrease in the voltage of the strongest module isdetected, since decreasing the duty cycle normally increases the modulevoltage.

In one embodiment, a target voltage for each module on the string can becomputed as a function of a ratio between the maximum power point powerPmp of the module and the maximum power point power Pmpm of thestrongest module. For example, the target voltage for a module can becomputed as Vm×Pmp/Pmpm, where Vm is the measured voltage of thestrongest module. The duty cycle of the module can be changed to drivethe module voltage of the module towards the target voltage, sincedecreasing the duty cycle normally increases the module voltage.

In one embodiment, the duty cycle for each local management unit ischanged to increase the current of the solar module attached to thelocal management unit (e.g., based on the measurement of the voltage andcurrent of the solar module), until the maximum current is achieved.This method assumes that string maximum power can be achieved with someaccuracy by driving each local management unit to maximum current. Inone embodiment, the voltages and currents of the solar modules aremeasured for tuning the duty cycles for maximum power point tracking forthe string. The measurements of the voltages and currents of the solarmodules also enable the local management units to additionally serve asa module level monitoring system.

The duty cycles can be adjusted by the system management unit (e.g.,1204) based on the measurements reported by the local management units(e.g., 1202 a, 1202 b, . . . , 1202 n), or adjusted directly by thecorresponding local management units (e.g., 1202 a, 1202 b, . . . , 1202n).

In one embodiment, during the process of setting and/or tuning the dutycycles, the maximum power point tracking operation by the inverter(1203) is frozen (temporarily stopped). Light intensity at the solarmodules is monitored for changes. When the light intensity at the solarmodules stabilizes, the voltage and current of the solar modules aremeasured for the determination of the duty cycles. Then normal operationresumes (e.g., unfreezing of maximum power point tracking operation).

In one embodiment, the local management units measure the voltages andcurrents of the solar modules to determine the power of the solarmodules. After identifying the highest power Pm of the solar module onthe string, the duty cycles of the solar modules on the string aredetermined by the power radio relative to the highest power Pm. Forexample, if a module produces 20 percent less power, it will bedisconnected from the string bus about 20 percent of the time. Forexample, if a module produces power P, its duty cycle can be set to1−((Pm−P)/Pm)=P/Pm.

In one embodiment, a predetermined threshold is used to select the weakmodules to apply duty cycles. For example, in one embodiment, when amodule produces power less than a predetermine percent of highest powerPm, a duty cycle is calculated and applied to the solar module. If themodule is above the threshold, the module is not disconnected (and thushaving a duty cycle of 100%). The threshold may be based on the power,or based on the module voltage.

In one embodiment, the system management unit (1204) finds the dutycycles for the local management units (1202 a, 1202 b, . . . , 1202 n)and transmits data and/or signals representing the duty cycles to thelocal management units (1202 a, 1202 b, 1202 n) via wires or wirelessconnections. Alternatively, the local management units (1202 a, 1202 b,. . . , 1202 n) may communicate with each other to obtain the parametersto calculate the duty cycles.

In one embodiment, the system management unit (1204) knows all thedifferent duty cycles indicated for the local management units (1202 a,1202 b, 1202 n).

In one embodiment, during power fine tuning, the system management unit(1204) sends the appropriate data/signal to the appropriate localmanagement units (1202 a, 1202 b, . . . , 1202 n), and then the systemmanagement unit (1204) calculates the total power of the string andcorrects the duty cycle to produce maximum power. Once maximum power isachieved, the duty cycles for the local management units (1202 a, 1202b, . . . , 1202 n) may be saved in a database and serve as a startingpoint for the corresponding local management units (1202 a, 1202 b, . .. , 1202 n) at the same time of day on the next day. Alternatively, alocal management may store the duty cycle in its memory for the nextday.

The stored duty cycles can be used when there is a fixed shade on themodules, such as a chimney, a tree, etc., which will be the same shadeon any day at the same time. Alternatively, historical data may not besaved, but may be recalculated from scratch on each run, for exampleevery 30 minutes.

In one embodiment, the light intensity at the solar modules is monitoredfor changes. The duty cycles are calculated when the light intensitydoes not change significantly. If there are changes in sun lightradiation at the solar modules, the system will wait until theenvironment stabilizes before applying or adjusting the duty cycles.

In one embodiment, the system management unit (1204) can communicatewith the inverter as well. When the environment is not stable (e.g.,when the sun light radiation is changing), the inverter may stop maximumpower point tracking. In such a situation, the inverter can be set upfor its load, instead of tracking for maximum power point. Instead ofusing the inverter to perform maximum power point tracking, the systemmanagement unit (1204) and the local management units (1202 a, 1202 b,1202 n) are used to set the operating parameters and balance the string.

Alternatively, when the environment is not stable but measurements andcalculation are done faster than the MPPT is working, there may be noneed to stop the MPPT on the inverter. Alternatively, when theenvironment is not stable, measurements can be taken few times for thesame radiation until a stable result is achieved.

Many variations may be applied to the systems and methods, withoutdeparting from the spirit of the invention. For example, additionalcomponents may be added, or components may be replaced. For example,rather than using a capacitor as primary energy store, an inductor maybe used, or a combination of inductor and capacitor. Also, the balancebetween hardware and firmware in the micro-controllers or processors canbe changed, without departing from the spirit of the invention. In somecases, only some problematic modules may have a local management unit,for example in a shaded or partially shaded or otherwise differentsituation. In yet other cases, local management units of strong modulesmay be virtually shut off. The methods for determining the duty cyclesfor the solar modules can also be used to determine the duty cycles ofgroups of cells connected via local management units in a string withina solar panel/module.

Enhanced Watch Dog

What is needed is a system and method for an enhanced “watch dog” devicethat can implement an emergency shut down of the solar panel system whenit detects a problem at the head end or in the wiring, thus maintainingthe system in a safe condition.

FIG. 18 shows an overview of an exemplary photovoltaic power system 2100known to the inventors. Photovoltaic solar panel (PVSP) 101 typicallyconnects via wires 2103, such pigtail wires, to a junction box 2102,which in turn connects the wiring 2104 to the wiring system, typicallyas part of a string of panels, or a high voltage box, to a combiner box(essentially a wiring panel) and from there on to an inverter feedingthe power grid. In this example the watch dog is in junction box 2102;in other cases the watch dog may be in other locations in the wiringfurther down the line, such as, for example, in the combiner box thatcombines wires of multiple panels and/or strings, or it may be in aninverter box that combines multiple wirings and the inverter.

FIG. 19 shows an overview of an exemplary photovoltaic power system 2200that is known to the inventors. Wires from the panel 2103 feed intoconverter or adaptor 2203. A controller 2204 is also present, whichcontroller communicates with a central controller 2109 (shown in FIG.10) as indicated by arrow 2206, in some cases via a wire line and inother cases wirelessly. Often a diode 2205 may be included for reversalof the panel, or if the panel has weak cells, to avoid reversal of thepanel. The configuration shown in FIG. 19 is typical of a stringconfiguration, but similarly it may apply in ac or other similarconfigurations, or high-voltage bus configurations, all of which areknown to the inventors. It is clear that in the case of an acconfiguration, diode 2205 would not be included in the system, becauseit would create serious problems.

FIG. 20 shows an overview of an exemplary system 2300 according to oneembodiment of the current invention. System 2300 is essentially anenhancement of system 2200, wherein the controller 2204 now hasadditional code 2308, which code performs the shut-down function of thecurrent invention. Also shown are several normally open or normallyclosed switches. Not all the switches are necessarily in all embodimentsof the current invention. For example, switch 2305 is used to short apanel. In this example it is shown as a normally open switch, controlledby controller 2204 (control line not shown). However, rather than amechanical switch, the on/off device could be typically a suitablesemiconductor device, including but not limited to a FET or MOSFET, orit could be an IGBT type of transistor that can take the current andshort the panel. Also, in some cases, rather than shorting the panel,the on/off device would create an active load to the panel and wouldallow a voltage to continue feed to the controller, as is shown by thefeeding line, even though the inverter or converter 2203 may be shutoff. Also shown is a switch 2304, which is normally closed. Again,rather than a mechanical switch, this could be a FET, MOSFET, or othersimilar suitable type of semiconductor switch. It is normally closed toallow the power of the inverter to flow out into the wiring; however, itcould go into a normal open state and thus disconnect the panel. In somecases, the converter or inverter 2203 may achieve the same functioninternally by managing switching devices already inside a converteraccordingly. Also, in some cases, switch 2307 may short the panelbypass. In particular, in the case of an ac system, where there is nodiode, a bypass may be desirable. In other cases, no bypass is desired,or, in the case of a high-voltage system a bypass may even be notdesirable. The shut-off may be triggered by, for example, the absence ofa regular signal from the main controller (not shown). In other cases,for example, a fault in the wiring, which can be detected by controller2204 by comparing different voltages, etc., may also automaticallytrigger a disconnect. In yet other cases, additionally, for example, theplus or the minus may be connected to ground to add security. In somecases, system 2300 may have a local capacitor or battery to power theunit even after loss of power from both sides.

FIG. 21 shows an exemplary process 2400 for implementation of the watchdog code 2308 according to one embodiment of the present invention. Inoperation 2402 parameters are initialized based on data from a storage2401 that would typically be an E2PROM in the device itself, and henceit could even survive loss of power. After initialization, in operation2403 the software executes local checks, which checks may includechecking that the wiring, voltages, and other components are correct andall signals present as they should be for normal operation. In operation2404 the software waits for a ping from the main controller. In somecases, the software may not wait for an incoming ping, but rather, itmay issue a challenge and receive a response to that challenge. Other,similar well known methods of two-way verification may by used. Atoperation 2405, the process branches. If the software receives aresponse it moves to operation 2407 to determine whether the response isa shut-down signal. If the response is not a shutdown signal (negative),the software loops back to operation 2403. If the response is ashut-down signal, the software moves to operation 2408, where it shutsdown the system and, in operation 2409, waits for a restart signal,after which it returns to operation 2402. If, in operation 2405, thesoftware does not receive a ping or other expected response within anallotted time, it moves to operation 2406, where it checks the number ofallowed skips. Depending on the circumstances, a certain number of skipsmay be allowed, particularly if the “heartbeats” of the ping are set ata high rate, such as 100 or even 1000 per second. In such cases, thesoftware may allow two, five, or even 100 skips (this limit is drawnfrom data store 2401) before it moves to operation 2410, where theprocess again branches. If the software receives a response before thelimit is reached (−), the process loops back to operation 2407 andcontinues as described above. If the software receives no response bythe time/count the skip limit is reached (+), the process moves tooperation 2408 and proceeds as described above. If the device has abattery, as mentioned above, it may remain in shut-down mode until iteither receives a restart signal or until the battery runs down, inwhich case it does a complete shut-down.

FIG. 22 shows an exemplary system 3100 according to one aspect of thesystem and method disclosed herein. Solar panels 3110 aa-nn areinstalled in multiple strings. The outputs of the strings are typicallyjoined in combiner box 3108, which then connects to inverter 3101, whichin turn connects to power grid 3109. As mentioned earlier, additionalhardware (not shown) such as relays or semiconductor switching elementswith an additional local controller may be provided, to allow eachstring to be powered up individually, thus reducing energy and powerneeded to poll panels or their respective local units. This exampleshows, for reasons of simplicity and clarity, only a single-phase powergrid, but the power grid could be a much larger and more complexmulti-phase power grid. Also shown is a master management unit (MMU)3102 (which is an example of a local system controller) and an auxiliarypower supply 3103, which connects directly to the power grid and whichcan, via feed route 3105, provide energy into MMU 3102. MMU 3102connects via lines 3107 to the dc wiring system and can, therefore, feedback dc current to the solar panel array, via the combiner box(es) 3108(only one shown) to the panels and their respective LMUs. In other casesan auxiliary power supply may connect directly to the dc wiring betweencombiner box 3108 and inverter 3101. Wiring 3106 allows the MMU 3102 tointeract with the inverter 3108 and, for example, suppress false startsof the inverter on the auxiliary voltage. MMU 3102 or some other,similarly suitable controller, may, for example, turn on only the dcvoltage every two or three minutes for a few seconds, thus sending justenough current to wake up the LMUs 3111 aa through 3111 nn in the panelsand allow them to do a quick query, each of their respective panels.Then if, for example, two minutes later, one of the units does notrespond to the query, the system would send an alarm indicating apossible security breach, such as a wire being cut or a panel beingremoved. In some cases, before sending an alarm, a re-test may be done,to verify that the alarm is caused by a non-responding panel, ratherthan just a temporary problem polling a unit. Also shown is informationserver 3121, which may belong to an operator of multiple sites withinformation directed to control specific sites. Additional servers 3140a through 3140 n could be, for example, emergency servers of a publicagency relevant to the location of the system, USGS earthquake monitors(relevant cases), etc. In some cases, information server 3121 maydownload information from these servers and then prepare it by locationand send a signal to MMU 3102 via a network 3104. In other cases, theMMU 3102 may pull that information directly from those servers.Controller 3130 controls multiple sensors 3131 a-n, which could be, forexample, smoke sensors, fire sensors, flow sensors, or other practicalemergency sensors.

FIG. 23 shows an exemplary process 3200 implemented by a softwareinstance residing in MMU 3102, according to one aspect of the system andmethod disclosed herein. In operation 3201 the program checks theoperating status of the MMU 3102. In operation 3202, the processbranches. If the unit is in standby operating mode (yes), the processmoves to operation 3203, where it ends. If the unit is not in standbymode (no), the process moves to operation 3204, where the programqueries information server 3121 for applicable local informationregarding possible events that warrant a shutdown or other controlchanges. Similarly, in operation 3205 the program queries emergencyservers 3140 a-n, and in operation 3206 it queries controller 3130 forinput from sensors 3131 a-n. In some cases the sensors may be connecteddirectly to the MMU 3102 through additional ports. In other cases theremay be multiple controllers 3130, and in yet other cases, MMU 3102 mayconnect to an existing fire alarm system controller, and pulling thefire alarm could also shut off power generation, for example, either forall or for part of a system. In operation 3207 the program checks, basedon some pre-existing values and rules, including, for example, location,ZIP code, and other information, whether any of the query resultsindicate a shut down anywhere in or in all the solar array. If no, theprocess moves to operation 3203, where the program ends. If yes, theprocess moves to operation 3208, where the program sends out commands tothe indicated units, which commands could shut down or disconnect theinverter 3101. (In some cases, an additional galvanic disconnect, notshown here, is provided outside the inverter.) In some cases the programalso instructs the LMUs to shut down, or in other cases the local powerremains available but an additional disconnect shuts off the remoteaspect. Also, in different cases, different actions may be taken. Forexample, if a local fire is indicated, some or all the panels in theaffected area may be turned off as a safety measure for respondingfirefighters, but the remainder of the system may be left working. Incase of an earthquake, as another example, a galvanic disconnect mayshut off the connection to the power grid 40-109, but, for example onlyif a sensor (not shown) determines that the supply line has been broken(i.e., no safe connection).

It is clear that many modifications and variations of this embodimentmay be made by one skilled in the art without departing from the spiritof the novel art of this disclosure. These modifications and variationsdo not depart from the broader spirit and scope of the invention, andthe examples cited here are to be regarded in an illustrative ratherthan a restrictive sense.

What is claimed is:
 1. A watchdog unit comprising: connectors to couplethe watchdog unit between a solar module and a power bus, the power busconfigured to connect a plurality of solar modules to an inverter; alocal controller configured to monitor a communication sent on the powerbus from a central controller remote from the solar module and determinewhether the communication has been interrupted for a time period longerthan a number of allowed skips; and at least one switch configured todisconnect the solar module from the power bus in response to adetermination by the location controller that the communication from thecentral controller has been interrupted for a time period longer thanthe number of allowed skips; wherein the watchdog unit is configured toconnect the solar module to the power bus when the communication is notinterrupted.
 2. The watchdog unit of claim 1, further comprising ajunction box housing the watchdog unit, the junction box to provideconnectivity between the solar module and the power bus.
 3. The watchdogunit of claim 2, wherein the local controller is configured to control aduty cycle of the switch to control an output voltage from the junctionbox.
 4. The watchdog unit of claim 3, wherein the local controller isconfigured to operate using power from the solar module.
 5. The watchdogunit of claim 1, further comprising a bypass circuit configured toenable current in the power bus to bypass the solar module when theswitch disconnects the solar module from the power bus.
 6. The watchdogunit of claim 1, wherein the watchdog unit is configured to determineirregularity in periodicity of the communication to determine whetherthe communication is interrupted.
 7. The watchdog unit of claim 1,wherein the communication is interrupted when a threshold ofirregularity is surpassed.
 8. The watchdog unit of claim 1, wherein thecommunication is interrupted when the central controller fails to send acommunication.
 9. The watchdog unit of claim 1, further comprising thesolar module; and a junction box coupled with the solar module toprovide connectivity to the power bus, wherein the watchdog unit residesin the junction box.
 10. The watchdog unit of claim 1, furtherconfigured to disconnect the solar module from the power bus when thewatchdog unit receives a shutdown signal.
 11. The watchdog unit of claim1, wherein the watchdog unit wirelessly communicates with the centralcontroller.
 12. A watchdog unit comprising: connectors to couple thewatchdog unit between a solar module and a power bus, the power busconfigured to connect a plurality of solar modules to an inverter, thewatchdog unit configured to: verify communication with a centralcontroller remote from the solar module; and shutdown the solar modulefrom the power bus if communication with the central controller cannotbe verified for a time period longer than a number of allowed skips. 13.The watchdog unit of claim 12, wherein to shutdown the solar moduleentails disconnecting the solar module from the power bus.
 14. Thewatchdog unit of claim 12, wherein to verify communication: a challengeis sent to the central controller; and a response to the challenge isreceived.
 15. The watchdog unit of claim 12, wherein to verifycommunication, a communication is received within a set time from when alast communication was received.
 16. The watchdog unit of claim 12,further configured to shutdown the solar module if a shutdown signal isreceived.
 17. The watchdog unit of claim 12, further configured to waitfor a restart signal.
 18. The watchdog unit of claim 12, furtherconfigured to draw energy from a backup energy source when a primaryenergy source is not available.
 19. A computer-implemented methodcomprising: monitoring, via a computing device, a signal from a centralcontroller remote from the computing device; determining, via thecomputing device, if the signal has been lost; disconnecting, via thecomputing device, one or more solar modules from a power bus if thesignal has been lost, the power bus configured to connect a plurality ofsolar modules to an inverter; waiting, via the computing device, for arestart signal; and connecting, via the computing device, the one ormore solar modules to the power bus when the restart signal is received.20. The method of claim 19, further comprising: enabling, via thecomputing device, a bypass circuit when the one or more solar modulesare disconnected from the power bus, so that current continues to flowin the power bus.